Musnad Ahmad 33:924

Muhammad ibn Bakr narrated to us, Ibn Jurayj informed us, Abu al-Zubayr informed me that he heard Jabir ibn Abdullah saying: I saw the Prophet, peace and blessings of Allah be upon him, throwing [pebbles at the Jamarat] while on his mount on the Day of Sacrifice. He was saying: "Take your rituals [from me], for I do not know, perhaps I will not perform Hajj after this Hajj of mine."